This invention relates to a device for synchronously rotating a plurality of spindles in disk drives used collectively as an information memory with each spindle used in driving a plurality of information memory disks.
It is possible to understand in connection with a device of the type described that a master reference is given by rotation of one of the disks that has a servo surface as a master disk and is driven by one of the spindles. Synchronized rotation of all disks is achieved in the disk drives by controllably rotating other spindles in accordance with the master reference. For this purpose, a slave reference is derived from rotation of one of the disks that is driven by each of the other spindles and has a similar servo surface as a slave disk. Such slave references are compared with the master reference to detect a phase difference between rotation of the master disk and rotation of each slave disk. The phase difference is used in controlling rotation of each of the other spindles to attain the synchronized rotation.
Such a device is disclosed in U.S. Pat. No. 4,907,105 issued to Fred Kurzweil, Jr., assignor to Maxtor Corporation, California. A similar device is revealed in U.S. Pat. No. 4,890,045 issued to Hiromi Ishizuka and assigned to the present assignee.
In a conventional device of the type disclosed in the Kurzweil or the Ishizuka patent, each of the master and the slave reference is given by an index pulse which is produced as each reference only once during one rotation of the master or the slave disk. Kurzweil and Ishizuka devices are excellently operable. It should, however, be noted that each reference is derived only once during one rotation of each disk. As a consequence, synchronized rotation is not precise depending on the circumstances. Furthermore, the synchronized rotation can not be rapidly achieved because a time interval of approximately one rotation of the disk is necessary to restore the synchronized rotation after out of synchronism is found in rotation of one of the other spindles.